This invention relates to oceanographic instrumentation, and more particularly to a device which cycles vertically and repeatedly between the surface and a desired depth in the ocean, i.e., profiling. Specifically, the present invention provides a means of reducing the energy expended during these profiles.
During observations of the ocean environment, it is desirable to use a vehicle able to drift freely (no physical connection to surface or bottom) and to both profile vertically and remain in equilibrium at predetermined depth.
During a descent-ascent profile, i.e., vertical ascent and descent, the properties of the surrounding water at all depths can be observed. At the ocean surface, stored data and vehicle position are reported to a shore station or ship, generally using communications via satellite. The trajectory of observed surface positions provides a measurement of ocean circulation.
It is desirable that the oceanographic vehicle and its observational payload be small and inexpensive. The vehicle should be capable of hundreds of profiles to a typical depth of 2000 meters (m) over a period of several years.
Commonly used profiler designs use an aluminum hull with an active buoyancy mechanism having a pump or displacer powered by an on-board energy supply. Examples of typical profiler devices may be seen in U.S. Pat. No. 5,283,767 (McCoy); U.S. Pat. No. 4,202,036 (Bowditch et al.); U.S. Pat. No. 4,202,034 (Bowditch et al.); and U.S. Pat. No. 4,191,049 (Bowditch et al.).
Most hulls designed to operate to 2000 m depth increase in buoyancy as their depth is increased. This characteristic facilitates finding a stable buoyancy at a fixed depth for deep drifting. When ascending, the active buoyancy mechanism must provide displacement to overcome decreasing vehicle buoyancy as it ascends. The minimal work required is the area shown to the right of the curve depicted in FIG. 2, i.e., [pressurexc3x97volume=work].
The present invention discloses an innovation which reduces the energy required to make vertical profiles, thus reducing the size and weight of the on-board battery and machinery, and increasing the performance envelope of the profiler. The present invention incorporates an entirely passive device which reduces the energy required to make vertical profiles. Specifically, the present invention adds a compensator to the hydraulic circuit of the profiler. The compensator stores energy by compression of gas during descent and releases the energy during ascent, thereby reducing the work required of the active buoyancy mechanism. The pressure from the external liquid medium in which the vehicle is submerged provides the energy, a portion of which is stored within the compensator.
These together with other objects of the invention, along with various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention.